The invention relates generally to tobacco curing and more particularly to a method of treating and curing tobacco leaves so as to have low levels of or no detectable tobacco-specific nitrosarnines and a reduced level of bacterial endotoxins as compared to untreated, cured tobacco leaves.
U.S. Pat. No. 5,040,550 to Argyropoulos and U.S. Pat. No. 4,448,208 to Friedrich et al. disclose processes of washing cured tobacco leaves or leaf pieces with both hot and cold water for extraction of resins, tar and nicotine as well as removal of pesticide residue.
It has been reported that air-cured and flue-cured tobacco contain tobacco-specific nitrosamines (TSNAs). See, xe2x80x9cEffect of Air-Curing on the Chemical Composition of Tobaccoxe2x80x9d, Anna Wiernik et al., Recent Adv. Tob. Sci, (1995), 21, pp. 39-80. According to Wiernik et al., TSNAs are not present in significant quantities in growing tobacco plants or fresh cut tobacco (green tobacco), but are formed during the curing process. Bacterial populations which reside on the tobacco leaves are stated to largely cause the formation of nitrites from nitrate during curing and possibly effect the direct catalysis of the nitrosation of secondary amines at physiological pH values. The affected secondary amines include tobacco alkaloids, which form TSNAs when nitrosated.
Star Tobacco and Pharmaceutical Co., Inc., has reported that it treats tobacco leaves before or during flue-curing by microwaving for purposes of reducing tobacco-specific nitrosamines. See WO 98/58555. The microwaving adds significant cost to the tobacco farmer, including the costs of excess handling and breakage of tobacco leaves, the microwave process, the microwave facility and the extra labor and time necessitated by the microwaving process. A further drawback to this method of reducing TSNAs is that microwaving of the tobacco leaves has a thermal effect upon the tobacco tissue resulting in heating of the tobacco leaves which may affect the taste and aroma of the smoke from the tobacco.
Because curing of tobacco leaves is normally performed by the farmer who grows the tobacco, a simple, economical and non-labor-intensive method of reducing the bacterial population and/or activity, TSNA levels and bacterial endotoxin levels of the cured tobacco leaves is desirable.
The present invention provides a method of treating tobacco prior to or during curing with an aqueous solution of bicarbonate or carbonate anions which is found to accelerate coloring of the tobacco during cure and thereby shorten curing time, particularly with Burley and other air cured tobaccos. When such treatment is coupled with the step of an immediate drying of the tobacco at conclusion of the curing process, the process achieves pronounced reductions in tobacco-specific nitrosamines and bacterial endotoxins in the cured tobacco leaves as compared to untreated cured leaves.
Accordingly, the present invention provides a method of treating air-cured tobacco with a wash solution of bicarbonate salt or carbonate salt, wherein the air-cured tobacco is cured in four weeks or less from the time of treatment with the wash solution, and has one or more of a reduced or eliminated amount of tobacco-specific nitrosamines, bacteria, bacterial activity and bacterial endotoxins. At the election of the practitioner, such air-cured tobacco may be selectively stripped from the stalk as the leaves turn brown during curing, and dried.
In another embodiment, leaf of Burley tobaccos or other variety of air-cured tobacco is primed at harvest, and the individual leaves are treated as described above, cured and dried so as to form cured leaves having a reduced or eliminated amount of tobacco-specific nitrosamines and bacterial endotoxins.
In another preferred embodiment, a tobacco leaf is treated with a wash solution of an antibacterial agent before or during curing, wherein upon completion of the curing process the treated tobacco leaf has a reduced or eliminated amount of tobacco-specific nitrosamines and bacterial endotoxins.